Low density open non-woven fibrous abrasive article



Nov. 1, 1960 H. L. HOOVER ETAL 2,958,593

LOW DENSITY OPEN NON-WOVEN FIBROUS ABRASIVE ARTICLE Filed Jan. 11, 1960 2 Sheets-Sheet 1 6r a m MJ /f EY Arm/Quays Nov. 1, 1960 H. L. HOOVER ETAL LOW DENSITY OPEN NON-WOVEN FIBROUS ABRASIVE ARTICLE Filed Jan. 11, 1960 2 Sheets-Sheet 2 [All [A fons F/sum' Z HOWARD L HOOVER Euszw: J DUPPI WAL 727? RAN/r/A/ er M 4% M AW A r TOR/1157s highly undesirable in many industrial buildings.

United States Patent LOW DENSITY OPEN NON-WOVEN FIBROUS ABRASIV E ARTICLE Howard L. Hoover, North St. Paul, Eugene J. Dupre, St. Paul Park, and Waiter J. Rankin, St. Paul, Minn., assignors to Minnesota Mining and Manufacturing Company, St. Pani, Minn.-, a corporation of Delaware Filed Jan. 11, 1 960, Ser. No. 1,453

13 Claims. Cl- 51-295) The present invention relates to non-woven fibrous abrasive articles of extremely open structure having an extremely high void volume (i.e., low density), which articles have a special utility in the floor maintenance trade, in hand scouring operations such as performed in domestic kitchens by homemakers, as well as in various industrial abrasive operations. This application is a continuation-impart of our copending application Serial No. 777,167, filed October 8, 1958, the latter and the present application both being a continuation-in-part of our copending application Serial No. 641,714, filed February 21, 1957.

Long prior to the present invention, for the past or 30 years, those engaged in the floor maintenance trade almost exclusively have employed rotary driven fiber brushes, or steel wool pads powered by rotary driving means, in the stripping or scouring of soiled wax or the like from floors, and in polishing ,previously laid waxes. Although various abrasive-containing constructions have been proposed from time to time, we know of none which heretofore has achieved any significant commercial acceptance in the floor maintenance field.

Notwithstanding the 'longperiod of years during which the floor maintenance trade has employed brushes and steel wool, such articles have many disadvantages. Brushes do not impart a sufficient abrasive action to be particularly useful in the commercial stripping of old wax or the like from floor surfaces. Further, they are difficult to clean after use. Steel wool, the more widely used article in floor scouring operations, has numerous significant drawbacks. Its abrasive action is limited. -It quickly becomes clogged with wax and residue, and is difficult to clean. Moreover, as the steel wool pad wears it invariably shreds metallic particles or tiny wires which are broken away and left on the floor surface. Unavoidably many of these escape removal insubsequent mopping,

operations. After subjection to moisture, residual particles of steel wool quickly: rust, even within a few hours or overnight, leaving unsightly diflicultly-removable rust stains many times their size on the floor. Additionally these small residual steel particles, which are very conductive, may lodge in contacts of sensitive electrical relays or other electrical apparatus, causing short-circuiting. Such particles are intolerablein hospitals-and also Steel wool pads also are subject .to snaggingor tearing when they bump against or come in contact with furniture legs, baseboard and the like. In so doing they tend to "roll up, becoming nonuniform and thereby rendering the pad prematurely useless. -In fact, steel wool pads ordinarily do not wear out completely, but either rust or become lumpy while much .of the original thickness remains.

The thickness of the conventional commercial steel wool pad necessary for suitable strength is about 1 /2 inches. This extreme depth allows detritus fromthe floor being cleaned to pass throughout the interior ofthepad 2,958,593 Patented Nov. 1, 1960 ice and be spun centrifugally from the pad edges. Baseboards, walls, etc., thereby are splattered and soiled to a height of several inches. Thus clean-up operations are materially lengthened and complicated.

These various disadvantages of steel wool pads have long been recognized in the floor maintenance trade. A further well-known disadvantage, however, and one of the most significant to economy minded commercial enterprises, is the slowness and incompleteness with which these prior commercial products strip or clean floor surfaces, and the long time required for cleanup after their use. This fact is evidenced by the cost of labor alone in ordinary floor maintenance which constitutes a disproportionate -90 percent of the total. Nonetheless, steel wool and brushes, used as above described heretofore have long continued to be virtually the only constructions widely employed in commercial floor scouring operations.

In spite of the disadvantages inhering in steel wool, fibrous abrasivecontaining articles as proposed from time to time have never become really commercially successful in replacing steel wool. Even so, fibrous structures of one sort or another, containing abrasive grains long have been known. For example, Hurst Patent No. 2,284,738 discloses a compressed aerodynamically formed fibrous mat impregnated with resin and abrasive mineral. In regard to such compressed fibrous abrasive structures,

see also Benner et al. Patent Nos. 2,284,715 and 2,284,716,

granted June 2, 1942, and Wescott Patent Nos. 1,668,475 and 1,668,476, granted May 1, 1928. Also, Loeffier Patent No. 2,327,199, granted August 17, 1943, discloses a stated substitute for steel wool, especially designed for kitchen use. Such references point away from and are antithetical to extremely open abrasive structures of extreme low density. For example, the Loefiier structure consists of a wad of long jute or sisal fibers impregnated apparently completely in the outer portions thereof with resin and abrasive. 'The inner portion of the pad is not impregnated with either resin or abrasive, so that a yieldable center cushion is provided for the purpose of allowing some resilience in the resulting structure. After impregnation, the structure is compacted, being molded or pressed to the ultimate shape desired, and cured. In sofar as we have been able to ascertain, the Loefiier structure has 'seen little or no extensive commercial use for the purpose desired, namely as a replacement for steel wool.

' Nothwithstanding the long-felt want and need, and notwithstanding any prior art, no one prior to our invention has provided the commercial floor maintenance trade with structures overcoming or avoiding the disadvantages above-enumerated inhering in presently commercially important floor maintenance or floor scouring structures. Our strutcures on the other hand, decisively and convincingly overcome and avoid these disadvantages and provide additional aflirmative advantages as well. They are finding wide commercial acceptance in replacing the long-used steel wool structures.

Inaccomplishing these and other important advantages, some of which will be specifically pointed out hereinafter, we provide a uniform lofty open non-woven three-dimensional lightweight web formed of many interlaced randomly disposed flexible durable tough organic ffibers which exhibit substantial resiliency and strength upon prolonged subjection'to wateror oils. Fibers of the web are firmly bonded together at points where they/intersect and contactone another by globules of an organic binder, thereby .forming a three-dimensionally integrated structure. Distributed within the web and firmly adhered by binderglobulesat variously spaced points along the Ifibers pected of such type of structure.

, tearing stresses applied to the structure in use.

are abrasive particles. The many interstices between adjacent fibers remain substantially unfilled by the binder and abrasive particles, there being thus provided a composite structure of extremely low density having a net- Work of many relatively large intercommunicated voids.

"These voids make up at least about three-quarters or four-fifths, and preferably more, of the total volume c cupied by the composite structure. Our structures are so open that in thicknesses of about one-fourth inch they are highly translucent or even transparent when held up to light, e.g., ordinary daylight, under condit ons where substantially all of the light registering on the viewers eyes passes through the structure. Additionally, the structures are flexible and readily compressible and upon subsequent release of pressure, essentially completely recover to the initial uncompressed form.

The resulting lightweight lofty extremely-open fibrous abrasive constructions exhibit a remarkably effective and unique abrasive action, contrary to What would be ex- They are essentially non-clogging and non-filling in nature, part cularly when used in conjunction with liquids such as water and oils. They can be readily cleaned upon simple flushing with a cleansing liqu d, dried and left for substantial periods of time, and then re-used.

The extreme openness and low density of the articles hereof are graphically ap arent upon reference to the accompanying drawing. Figure 1 of the drawing is a photographic reproduction. greatly enlarged as indicated, of one form of our low densty abrasive structures showing globules of resin or adhesive binder bonding the fibers together at points where they cross and contact one another thereby to form a three-dimensionally integrated structure. Embedded within the globules and thereby bonded firmly to the fibers are abrasive particles. which can be seen upon a close inspect on of the resin globules in Figure 1. The interstices between the fibers are substantially unfilled by resin or abrasive, the void volume of the structure depicted exceeding 90 percent. In fact it is apparent that impregnation (as that term normally is employed) of the web by the binder and abrasive does not occur. A tri-dimensionally extending network of large intercommunicating voids extending throughout the article is defined among the treated fibers. The fibers in large part uncoated or only extremely thinly coated, are resilient and vieldable, permitting the structure to be extremely flexible and vieldable, whereby the abrasive particles are extremely effective.

Figure 2 of the drawing 's a photographic cross-sectional view, enlarged as indicated, of another form of our invention which is particularly suited as a floor stripping or scouring pad. In this structure the fibers are bonded at their crossing points by two distinct types of binder, each existing in the structure in the form of globules. The darker globules situated generally in the lower half of the depth of the structure consist of a relatively hard r gid binder containing and adhering abrasive grains to the resilient fibers. The lighter billowy appearing globules disposed generally in the upper half compr se a resilient rubbery binder material having very high resistance to The structure is extremely open and of low density throughout, with intercommunicat ng voids being defined by the fibers and abrasive mineral-rigid binder and rubbery binder.

In fact, the structure depicted has a void volume of about' 90 percent. As in the structure of Figure 1, when held up to the light so that substantially the only l ght rays registering on the eyes of the viewer pass through the structure, it is remarkably translucent and nearly transparent, even through it has a thickness of about one-v tures has been found to be of substantial importance. Preferably the void volume is maintained within the range of from about 85 percent to at least about 95 percent. Structures wherein the void volume is somewhat less than 85 percent are useful for our purposes though not ordinarily recommended. On the other hand, where the void volume is decreased below about 75 percent, it has been found that the outstanding and advantageous properties diminish rapidly. For example, the ready fiushability or cleanability of the floor scouring structures, and therewith the abrasive cutting rate, etc. drops off. Notably, the extreme translucency drops off rapidly at such lower ranges of void volume and openness.

We prefer to form the web component of our combination structures from synthetic fibers such as nylon and polyesters (e.g., Dacron). The uniformity and quality of such types of fibers can be closely controlled. Also, these fibers retain substantial of their physical properties when wet with water or oils. Various natural fibers which are flexible, resilient, durable and tough, can also be utilized. For example silk thread has been found suitable, and horsehair is also useful for some applications.

' On the other hand, since the structures hereof often are subjected to water and/or oils, fibers should be selected which maintain substantial of their essential characteristics under subjection to media to which they will be exposed in the desired particular use. Cellulose acetate, and viscose rayon fibers have been found, for example,

' to demonstrate poor wet strength characteristics and are should be taken against embrittling penetration of the composite fiber by the binder resin. Such can be prevented, for example, by sizing the composite, or by employing a high degree of twist therein.

By and large, the length of the fibers which may be em ployed is dependent upon the limitations of the processing equipment upon which the non-woven open web is formed. In forming this component of our novel combination we prefer the Rando-Webber and Rando-Feeder equipment (marketed by the Curlator Corp, Rochester, N.Y.), variously described in Buresh Patents No. 2,744,294, No. 2,700,188 and No. 2,451,915 and Langdon et al. Patent No. 2,703,441. With such processing equipment, fiber length ordinarily should be maintained within about one-half to four inches, the normal length of one and one-half inches being preferred. However, with other types of equipment, fibers of different lengths, or combinations thereof very likely can be utilized in forming the and three-dimensionality in the web it is preferable that I use. Q Weft F sh exhibit a r ther l w coeflicient of friction in all or a substantial amount of the fibers be crimp-set. However, crimping is unnecessary where fibers are employed which themselves readily interlace with one another to form and retain a highly open lofty relationship in the formed web.

Many types and'kinds of abrasive mineral binders can be employed. In selecting these components, their ability to adhere firmly both to the fiber and abrasive mineral employed must be considered, as well as their ability to retain such adherent qualities under the conditions of Generally, it is highly preferable that the binder absence the, e.g., they do not become pasty or sticky in response to frictional heat. In this respect relatively hard rigid resin compositions seem best. However, some materials which of themselves tend to become pasty, e.g., rubbery compositions, can be rendered useful by appropriately filling them with particulate fillers. Binders which have been found to be particularly suitable include phenolaldehyde resins, butylated urea aldehyde resins, epoxide resins, polyester resins such as the condensation product of maleic and phthalic anhydrides and propylene glycol.

Amounts of binder employed ordinarily are adjusted toward the minimum consistent with bonding the fibers together at their points of crossing contact, and, in the instance of the abrasive binder, with the firm bonding of the abrasive grains as well. Binders and any solvent from which the binders are applied, also should be selected with the particular fiber to be used in mind so embrittling penetration of the fibers does not occur.

Having described our novel structures generally, the same will now be further illustrated, and the manner in which they can be produced will be shown, all with the aid of the following specific examples.

Example I This example describes the manufacture, under commercial conditions, of a floor scouring pad, such as that depicted in Figure 2 employing two types of binder. An abrasive and binder slurry is first prepared in accordance with the following formulation:

March 29, 1955) A-stage basecatalyzed phenol-formaldehyde resin having a phenolzformaldehyde mol ratio 1:1.8 (82% nonvol-atiles 109 Cellosolve (ethyleneglycol monoethyl ether) solvent 82 Grit 180 silicon carbide abrasive mineral 140 Total 341 The phenol-aldehyde resin is added to a stainless steel pressure tank liner having about a 50 gallon capacity, following which the solvent and Versamid resin are added. The contents are then thoroughly mixed with a high speed propeller mixer, e.g., a Lightnin mixer. The viscosity of the binder composition is then adjusted to 150-190 cps. at 75 F. by the further addition, as necessary, of Cellosolve solvent. The tank liner is then positioned in a pressure tank, which is equipped with a motor driven agitator, and the tank covered. Agitation is then commenced, during which time the abrasive mineral is added, following which the tank is sealed. Agitation is continued during the subsequent application of the tank contents to the web, as will be shown.

A rubbery adhesive binder composition is also prepared. Two hundred pounds of a rubbery butadieneacrylonitrile copolymer latex (40 percent solids by weight) the butadiene:acryloni-trile ratio being about 60:40 (available from the B. F. Goodrich Co. under the trade designation Hycar Latex 1561) are added to a 50 gallon capacity pressure tank. Also added are accelerating, stabilizing and curing agents for promoting cure of the copolymer to a stable resilient rubbery condition under the cure conditions specified hereinafter. The tank is then covered and sealed. Agitation is commenced, thereby causing thorough mixing of the ingredients, agitation being also continued as the batch is used.

The two pressure tanks containing the respective adhesive compositions are closed and pressurized to an application pressure in the order of about 20 lb./in. gauge. The pressure tanks containing the abrasive-containing slurry and the rubber adhesive composition respectively are connected to spray heads in different spray booths, as more fully described hereafter.

A lightweight 40-inch wide open non-woven air laid web is then formed on a Rando-Webber machine, commercially available from the Curlator Corporation of Rochester, New York. The web is formed of 15 denier (45 micron diameter) crimp-set one and one-half inch staple nylon fibers. Initially the fibers are fed into a conventional garnett machine to loosen and to separate the fibers from the strands in which many exist as received from the manufacturer, this preliminary step being highly desirable but not essential. The loose staple from the garnett machine is then transferred to the feed box of the Rando-Webber machine, the feed box being kept approximately one-fourth to three-fourths filled in the interest of uniformity of the web. The machine is then star-ted and adjusted to form a random web having a weight within the tolerance limits of l820 grains per 4 inch by 6 inch section.

When the Rando-Webber machine is producing a uniform open web within the desired tolerances, the web from the machine is led onto a continuous conveyor belt system where it passes through a spray booth, the-upper surface of the web being there continuously sprayed with atomized resin-abrasive slurry. Within the booth at a distance about 3 feet above the web are disposed multiple spray nozzles, mounted to reciprocate across the web perpendicularly to the direction of web movement. Since these spray nozzles are connected to the pressure tank containing the resin-abrasive slurry, they are provided with abrasion-resistant tungsten carbide tips, the nozzle apertures being 0.064 inch.

In the present example the web is formed at a constant speed of about 10 feet per minute and is supported by a conveyor moving at the same rate. Adjustments in spray weight are made by adjusting the air pressure in the pressure tank, which in turn permits variation in the amount of slurry passing through the nozzles onto the Web. The size of the slurry droplets is controlled by varying the atomizing air pressure at the nozzles.

The pressure in the tank containing the resin-abrasive slurry is adjusted so that 76-83 grains on a dry weight basis per 4 inch by 6 inch section are applied to the web. The number of nozzles employed can be varied so as to permit the tank pressure to be maintained within convenient limits, e.g., between about 9 and 30 pounds per square inch gauge. -In the operation being described two nozzles ordinarily are suitable.

The laterally reciprocating spray heads provide uniform coverage for the web across its entire width.

After being sprayed, the web is passed through a 20- foot drying and curing oven equipped with banks of infrared lamp units of variable intensity at each end of the oven, and provided with a hot air supply. Air at a temperature of about 300 F. enters at the center and is withdrawn at both ends of the oven. It should be understood, of course, that these operating conditions may not hold for ovens of different size or length, or where the rate of travel of the sprayed web is substantially different than that here employed.

In any event, however, oven conditions preferably are adjusted so that the emitted treated web is non-tacky to the touch while still warm, and yet the globules of resin applied to the web fibers do not appear to be heat blistered, upon microscopic examination.

After passing from the oven, the web is inverted and placed on a second conveyor belt, the untreated surface of the web now being upwardly disposed. The web is then led into a second spray booth, similar to the first, where the rubbery composition is applied to the web through laterally reciprocating nozzles. Spray weight of this treatment is maintained at 4S55 grains per 4 inch by 6 inch section on a dry basis.

Next the web is led through a second 20-foot long oven similar to and positioned immediately above the first, the rubbery treatment being dried and partially vulcanized or cured to a non-tacky state, care being taken to avoid blistering of the rubber globules, which may result if the web is heated at too high a temperature or for too long a time.

The product continuously formed as described, is wound upon inch diameter wire mesh cores in lengths of 100l25 yards. Each roll is then heated in an oven for about 13 additional hours at a temperature of from 210-220 F., as determined by thermocouples placed along the center of the cores, to complete the cure of the resin constituents. Following cure, the product is cut into desired sizes, and packaged for shipment in commerce.

The resulting composite has a thickness of about onefour-th inch. It appears grey on the side where the resinabrasive slurry composition was incorporated, and the rubber treatment on the reverse side appears white or slightly off-white. Void volume is 90 percent. When the pad is held up between the eye and a source of light it is highly translucent. That is, objects are clearly visible therethrough indicating many unobstructed paths through the pad thickness. In fact, when the pad is held very close to the eye, thus eliminating nearly all light registering on the eye which does not pass through the pad, it appears to be virtually transparent. When held under a water faucet, a fairly rapid water stream passes through the pad nearly unobstructed. The pad is flexible and can be crumpled and folded much like a wash cloth and then spread out flat to its original state. Although the abrasive surface of the pad is rough to the feel, it is not annoyingly so. Even though the respective binder compositions are sprayed on the web in rather small amounts, the binder globules (containing abrasive particles in the case of the abrasive binder) collect at and adjacent at least a substantial number of points where the fibers cross in contact, thereby to form the three-dimensionally integrated structure.

The composite construction of the present example, has a particular utility as a rotary floor scouring pad. For such use the pad is employed in disc form. In floor maintenance operations, the abrasive surface of the pad is placed on the floor to be cleaned and a driving pad rotatably powered by any conventional rotary floor maintenance machine is placed on top. The face of the driving pad in contact with the rubberized surface of the pad preferably is composed of a resilient material and is provided with numerous flat-surfaced blocky resilient protuberances, the pad-engaging surfaces thereof lying substantially in a common plane. Channels are defined by the protuberances with the channels extending to the periphery of the driving pad.

In a conventional floor scouring operation a scrubbing solution, e.g., a soap solution, is spread and the rotary floor maintenance machine driving the scouring pad is passed immediately over the wet area. Following the pass with the machine, the cleaned floor is rinsed with a mop and allowed to dry.

It has been found that by employing the floor scouring pad of the present example in place of a conventional steel wool pad in the stripping of old wax from floors, such as in industrial and public buildings, a time saving in the order of 35 percent or more results. Since the cost of labor is in the order of 85 percent of the total, the use of our structure permits a reduction in the order of 30 percent of the entire cost of the floor maintenance operation. With our pads automatic floor maintenance machines can be used at peak efiiciencies. Operator fatigue is reduced. Moreover, the quality of scouring has been found to be greatly superior to that obtained using conventional steel wool structures. For example, accumulations of years of wax and dirt have been removed with the aid of only a single or double pass with our floor scouring structures, where heretofore it was deemed necessary to scrape the floor by hand with implements such as putty knives.

Materials stripped from the floor are quickly flushed with the cleaning solution through the open network of the abrasive structure and away, due to centrifugal force. In this respect the channels between the protuberations of the driving pad provide flow paths facilitating emission of the detritus. In any event, our structures thus are extremely resistant to filling or clogging.

The scouring pad being rather thin, i.e., in the order of about one-fourth inch uncompressed, there is little or no spattering on walls, baseboard, furniture, etc. during floor maintenance operations.

No residue of pad fibers or fragments worn away during the operation is ordinarily visible on the floor. Nor do rust spots appear after a cleaning operation. The pad is thus extremely effective in the cleaning or scouring of light colored linoleum, rubber or vinyl tile surfaces, although it is equally suitable for terrazzo, hardwood and other types of floors.

Although our floor scouring pad is extremely aggressive in removing soiled accumulated wax coatings, we have found that it does not substantially abrade, scratch or wear the actual floor surfacing, i.e., tile, varnished wood, etc. In fact, the difference between the extreme aggressiveness toward the wax and toward the cleaned floor surface is so marked as to be audibly distinct to a skilled floor maintenance operator. Thus he knows when the floor he is scouring is completely cleaned of soiled wax preparation.

When the floor stripping operation is completed, the pad, if not worn out, is simply rinsed out in a wash bucket, or under a faucet, wrung out like an ordinary wash cloth and allowed to dry, as by hanging over the side of the wash bucket. Following drying, the pad is capable of being re-used the next day or even weeks or months later. It does not become sour, unsanitary or rusty.

The floor scouring pads of the present example, notwithstanding their flexible, almost flimsy, appearance, also demonstrate long life, and often can be employed to scour 8,000 to 10,000 square feet of floor surface before being worn out. The pad wears uniformly thereover, becoming thinner and thinner until only the rubbery treated skeletal structure remains; yet, as above stated, no residue of components is ordinarily visible as the structure wears through use.

The presence of the rubber treatment on one side of the structure of the present example has been found to increase materially the resistance of the structure to tearing and shredding when it bumps or rubs against baseboards, furniture legs, etc., when in use. Of course, lesser or greater amounts of the rubbery material can be applied in the top portion of the pad structure. It is noted that where greater amounts are employed the void volume of the rubber treated portion is correspondingly reduced; but in any event the high void volume and openness will remain in the abrasive portion of the structure. Or, such rubber treatment, though generally preferred in the floor scouring structures, may be eliminated. This may be done, for example, by appropriately selecting binders having the character of imparting high tear resistance to the web while still being hard and durable binders for the abrasive. In such instances, the pad is then treated throughout with abrasive binder and mineral. However, binder materials which firmly and adherently bond abrasive grains to the web fibers ordinarily are quite hard and rigid (e. g., the plasticized phenolic resin of the present example has a Knoop hardness number of 38) and tend to impart lower tear resistance to the resulting structures than do softer more resilient binder materials such as rubbery binders, which characteristically have Knoop hardness numbers of one or less.

In various structures hereof other than the floor scouring pads, the rubber treatment preferably is eliminated. The floor polishing (as contrasted with stripping or scouring) structure of the following example illustrates such a product of our invention.

9 Example II An abrasive binder slurry is first prepared in accordance with the following formulation:

Weight percent Liquid epoxy resin (Shell Epon 828) a reaction product of bisphenol A and epichlorohydrin having an epoxy number of about 190 grams per epoxide equivalent and a hydroxy number It has been found desirable to mill the pigments with about half the epoxy resin prior to adding it to the tank liner. Subsequent mixing then disperses the pigment particles uniformly throughout the slurry.

A lightweight 40-inch wide lofty, open, non-woven airlaid web, like that described in the previous example, is

formed of 15 denier crimp-set one and one-half inch nylon staple. The continuously formed web is then led through a spray booth as before, where the previously prepared resin-abrasive slurry is added uniformly at a dry coating weight of 38-45 grains per 4 inch by 6 inch section. The treatment is then dried and cured to a non-tacky state as described in connection with Example 1, following which the web is inverted and led through a second spray booth where the opposite web surface is sprayed with the resin-abrasive slurry at a dry coating weight of 38-45 grains per 4 inch by 6 inch section. The thus treated web is again passed through an oven as before, where the second treatment is dried and cured. The resulting product is then taken down by winding in lengths of about 300 yards on 3-inch paper cores. Following this it is unrolled and cut to the desired size and shape and packaged, etc. for shipment in commerce.

The resulting product is light tan or beige, and although the surfaces thereof feel coarse, they are not annoyingly scratchy. It is clearly translucent when held to the light. In fact, when held quite close to the eyes so that the only light registering on the eyes passes through the structure, it is very nearly transparent even though it is somewhat in excess of one-fourth inch in thickness. Void volume is about 92 percent. The product is extremely flexible, and its extreme openness is further demonstrated by the fact that when held under a water faucet, the stream passing through the thickness thereof is virtually unobstructed.

The pad, like the fioor scouring pad described in connection with the preceding example, is preferably used with floor maintenance equipment provided with a protuberated rotary driving pad. After the wax applied to a previously cleaned floor has dried, the pad is used to buff the resulting wax surface. The finer abrasive mineral of the present example is less aggressive than that of the floor scouring pad, and the present pad serves to polish the previously laid wax to a high luster. Again, no visible residue of worn pad fibers is left, and no rust spots or stains subsequently appear on the fioor. After a polishing operation, or between operations, as for example, where a single pad is used to polish different types of waxes in succession, the pad is merely flushed out under a faucet, or in a soapy wash bucket and rinsed, and then wrung out to dry. Useful life is long, as much as 100,000 square feet of floor polishing for a single pad being not unusual. The pad can be used day after day or over periods of weeks or months without becoming sour, lumpy or unsanitary.

The abrasive binder of the present example, having a Knoop hardness number of about 13 when cured, is

somewhat softer than that of the plasticized phenolic composition of Example I. Since the conditions to which the floor polishing pad is subjected ordinarily are less rigorous than in the case of the stripping or scouring pad, and since the abrasive mineral is finer, a somewhat softer abrasive binder can be tolerated in the former. In fact, a slightly softer resin may even be advantageous in that it exerts a milder, less abrasive, influence on the surface to be polished. In any event, however, resin compositions having a Knoop hardness number exceeding about 10 are recommended; and a substantial increase in softness of resin compositions with corresponding decrease in effectiveness, occurs at Knoop values ranging from about 8 down to 6.

Extremely effective scouring pads for use in the kitchen are also provided by our invention. These are similar in construction to that of the present example, rather fine abrasive grains preferably being used. A commercial pad having a size of 4% inches by 7 inches by A inch utilizes grit 320 aluminum oxide mineral in conjunction with the abrasive binder of Example I, the resulting open pad having a void volume of about 91. percent. Our kitchen scouring structures enjoy many of the same advantages over steel wool (by far the widest commercially employed kitchen scouring structure heretofore employed) in the floor maintenance field. They are superior in aggressiveness without being overly scratchy. They do not rust and are extremely easy to clean simply by flushing out in a dish pan or under a faucet. They can then be wrung out dry and re-used without becoming clogged with unsanitary decomposable food matter. Indeed, our kitchen scouring structures are so readily cleaned and sanitary, they can alternately be employed in scouring dirty pans and in cleaning and scraping food, e.g., carrots, in preparation for eating, with only a single washing necessary in between.

The articles hereof can be employed in conjunction with additional elements attached thereto, e.g., backing elements such as sheets and/or hand blocks, and effectively used as scrub brushes and the like and for a variety of other purposes.

Our novel abrassive articles are also highly suitable for various industrial abrasive uses. A readily conformable, compressible rotative abrasive wheel structure has long been sought which will fill the gap in commercial continuous metal finishing processes, between the primary cleaning and abrading operations (performed, for example, with coated abrasive belts), and the final polishing operations (using fine buffing wheels). Heretofore, abrasive wheels formed from cloth discs mounted on a shaft and coated on their periphery with adhesive and abrasive mixtures have been employed largely in these important intermediate abrading operations. Such wheels are extremely dirty in operation, require high abrading pressures, and must be frequently re-treated with abrasive and adhesive. Rotary brushes also have been used, but exhibit a very low abrasive aggressiveness, and often bristles fiy therefrom endangering the operator. The structure of the following example is highly suited commercially for these operations, without the disadvantages of prior structures.

Example 111 -of grit silicon carbide in 60 parts of a 49% solution of A stage phenol-aldehyde resin in ethylene glycol monoethyl ether (Cellosolve). The phenol-aldehyde resin had a phenolzformaldehyde mol ratio of about 1: 1.8,

the manufacture of coated abrasives. .Knoop hardness number of about 45. The spray nozzle and was made using a basic'catalyst. Resins of this general type are frequently used as bond adhesives in They exhibit a had an aperture of .064 inch and was made of tungsten carbide to minimize wear caused by the abrasive slurry.

.The treated skeletal structure Was precured in a 205 F. oven for 1 minute, inverted, and an additional 12.7 ounces per square yard of the same mineral-resin slurry applied to the opposite surface. The abrasive-included skeletal structure was further precured at 205 F. for 1 minute, after which time it was still somewhat tacky to the touch. It had a thickness of about /3 inch.

Six discs having a diameter of 12 inches were then cut from the precured tacky skeletal structure. These discs were superposed, compressed against stops to an overall thickness of 1 inch, and cured and thereby unified in this mildly compressed form at 250 F. for 16 hours, at which time the total weight of the composite abrasive wheel was 324 grams. Void volume was about 89 percent. Of the solid materials about 31% was silicon carbide, 56% was adhesive, and 13% was composed of the fibrous members, on a volume basis.

A l /z-inch center hole was cut in the 1-inch x 12- inch wheel, which was then mounted on the shaft of a 230 volt 5 horsepower backstand grinding machine and rotated at 2000 r.p.m., i.e., 6280 s.f.p.m. Because of the wheels extremely light construction, it was not necessary to provide complex operating hardware for mounting and truing it, the only equipment used consisting of two 8-inch diameter x 45-inch thick steel flanges, one of which was mounted on each side of the Wheel. A sharp-lipped stainless steel tray covered with oxide film and having nicks and scratches present on its surface was then applied against the periphery of the rotating wheel. One thorough pass of our wheel across the surface of the metal removed the visible oxide film and produced a fine satin finish. A total of 20 trays was satin-finished in 10 minutes without visible Wheel wear and with no apparent differences in quality of finish. In contrast, the conventional method of finishing the stainless steel tray involving the use of greaseless polishing wheels requires at least 5 minutes reloading and drying the wheel every 10 minutes of useful finishing time, during which only about trays can be finished. Not only does the finish obtained by this prior method vary in quality as the set up coating wears and the rate of cut decreases, but no single tray has a finish as uniform and attractive as that obtained using our wheel.

Our wheel was also used to impart attractive and uniform satin finishes to aluminum frying pans, brass door knobs, copper tubing and cold rolled steel bumper guards having very complex curvature. It was also extremely useful in performing such difficult operations as the cleaning of rusty bolt threads and the removal of mild mill scale from cold rolled steel flat stock. When the work-pieces were advanced in the direction of wheel rotation, we obtained a satin finish; i.e., the surface was uniform, smooth, and diffusely reflective. When the work-pieces were advanced in a direction opposite to that of wheel rotation a sand blast finish characterized by many short, small peened impressions was obtained. We know of no other finishing device having this versatility.

It will be observed that the wheel of the present example is a laminated structure. By forming the constructions hereof in a rather narrow thickness, i.e., in the order of one-fourth inch, distribution of the adhesive binder abrasive mineral throughout is insured. Where more depth is required, several layers or thicknesses are laminated.

It should be noted, however, that by employing techniques other than spraying, somewhat greater thicknesses of web may be suitably treated in forming our structures. In fact, roll coating, dip coating, separate application of adhesive and mineral, etc., may have advantages over the spray application described in the previous examples. For instance, spraying the adhesive first and then sifting in the abrasive separately is particularly suitable for incorporating coarse mineral (e.g., grit 50 or larger), and also results in products of slightly different abrading characteristics. It may also be desirable to employ one type hinder or means for adhesively bonding web fibers together to integrate and unify the web and a grit binder of different composition for bonding the mineral grains to the integrated and unified web. Light treatments of elastomers such as polychloroprene, Buna N compositions, etc. serve well for unifying the web fibers when a separate grit binder is to be used. Whatever the method and materials employed, however, care should be exercised to maintain the extreme openness of the structure in accordance with the teachings hereof.

In Example III 15 denier l /z-inch nylon staple was employed for the industrial abrasive wheel structures. For instances of other industrial abrasive uses, attention is directed to Examples 2, 3 and 4 of our parent application Ser. No. 641,714 where 1-3 inch 60 denier nylon, 1 /2-inch 60 denier Dacron polyester fiber (using a cured epoxy abrasive binder) and 3-inch 15 denier nylon, respectively, are employed.

As previously mentioned, the properties of the fibrous component of our open low density abrasive articles can be modified, altered and/ or bolstered, as desired, through appropriate treating or coating of the fibers. Such treatment can be imparted either to the fibers themselves, to the lofty Web prior to the addition thereto of abrasive particles and binder, or to the low density abrasive product typified in the preceding examples and as disclosed in our parent applications Serial No. 641,714 and Serial No. 777,167. It has been found that the properties of the otherwise completed product hereof can be substantially enhanced by appropriately treating it with various resinous or polymeric materials. For instance, by such treatment the useful life of floor maintenance and industrial abrasive articles hereof can be multiplied several times.

The treatment can be applied in liquid form utilizing known coating or spraying techniques followed by a hardening and/ or curing of the treating or coating materials in place. Embrittlement or filling of the article by the treatment is to be avoided. In order best to distribute the treating material throughout the structure, it is preferable (but not essential) to employ an expandable composition, i.e., a composition which can be foamed. In such case the treating material is lightly applied, for example, through dip coating techniques followed by removal of excess with squeeze rolls, the resin subsequently being caused to foam and cure or harden in place. During foaming the resin expands and forms a thin coating about and around substantially all of the solid components of the abrasive-containing web. Due to the modest amount of material applied and to the rupture of the cells of the foam as the material. passes through the interlaced fiber structure, the resulting thin resin coating is largely continuous and non-cellular. In any event, whether an expandable material is or is not employed, the openness and high void volume of the article should not be significantly reduced. 7

The treating material, when dried or cured, firmly bonds to the components of the structure and particularly to the web fibers. It is tough, flexible and resilient in thin coatings 101' films, preferably being no harder than the abrasive grit binder, and is non-smearing under contemplated conditions of use. Where desired as an extender or to enhance the properties thereof, the treating material can be filled. Preferred treating materials inelude polyurethane resins or polymers, such as those prepared by reacting a polyisocyanate, e.g., an aromatic polyisocyanate, with polyethers, polyester and polyester amides. One such polyurethane system comprises a blend of, by weight, 6 parts of high molecular weight 13 (about 2,000) polypropylene glycol (Union Carbide fNiax PPG-2025), 2 parts high molecular weight (about 3,000) propylene oxide-modified glycerine (Union Car- .bide Niax LG-56), and 3 parts tolylene diisocyanate. This polyurethane can be cured utilizing heat and/or accelerators such as N-methylmorpholine, and, as is preferable, can be caused to foam and cure by the appropriate use of accelerators and water or equivalent foaming agents. Another example of a highly satisfactory polyurethane system comprises the foamable prepolymer of aromatic polyisocyanates reacted with a diglycolic acid-modified castor oil resin, employed as described in Harrison et al. application Ser. No. 642,967, filed February 28, 1957, now Patent No. 2,921,916, granted January 19, 1960. Other treating resins which can be employed without being expanded, or which can be foamed bythe use of appropriate blowing or foaming agents, include epoxy resin compositions (such as the epoxy-Versamid composition disclosed in Example II), soluble nylon resins (Du Pont Zytel 61), highly vulcanized elastomers such as polychloroprene, and alkyd resins such as melamine modified alkyd resins.

The post treatment of our materials just described can also be advantageously utilized in the manufacture of our laminated open low density abrasive articles. The ad vantages of the post treatment can be fully attained while at the same time avoiding the undesirable presence of resin parting lines between laminae. After complete formation of the low density abrasive web, the treating material is applied to the web before the multiple layers are assembled, e.g., before several sheets or discs are laid up or before the web is wound convolutely upon itself. After assembly the treating material is caused to foam, cure or harden in place, the several laniinations being thu firmly united by the treating materials to form a highly satisfactory composite article.

In describing our invention, we are aware that lofty batts formed of various fibrous materials have long been employed for upholstery stufling, insulation, filters, etc. Indeed, such materials have been known for over 35 years. Such early batt materials have been treated with an adhesive to strengthen the fibrous structure. For example, see Wescott Patent No. 1,646,605, granted October 25, 1927, on application filed November 18, 1922; and Weber et 21. Patent No. 1,906,028, granted April 25, 1933.

More recently, at least prior to October 1950, the Curlator Corporation of Rochester, New York, manufacturers of the RandoWebber machines for laying or forming non-woven fibrous mat materials, distributed a pertinent printed publication entitled Rando-Webber Rando-Feeder Machines Bulletin No. 101. In this bulletin are disclosed non-woven heavy mats, industrial non-woven fabrics, wadding, felt and household non-woven fabrics which can be manufactured on the described Rando- Webber machine from various materials such a reclaimed tire cord, cotton linters, garnetted cotton clips and Wool Waste, cotton mill waste, acetate and viscose rayon, or nylon. Adhesive materials suitable generally for bonding web-fibers are disclosed, including polyvinyl acetate, polyvinyl chloride, rubber latex, reclaimed rubout said web, and abrasive particles distributed within Said weband firmly bonded to web fibers by a relative- 14 ly hard rigid binder, interstices between adjacent fibers being open and substantially unfilled by adhesive binder or abrasive, there being defined throughout said article a tri-dimensionally extending network of intercommunicated voids constituting at least about 75 percent of the volume of said article, said article further being flexible and readily compressible, and upon release of pressure, capable of recovering substantially completely to its initial uncompressed form.

2. An abrasive structure comprising several layers of the low-density abrasive article of claim 1 in unified laminated form.

3. The open low-density abrasive article of claim 1 in unified convolute form.

4. An open low-density abrasive article comprising a uniform lofty open non-woven three-dimensionally in tegrated fibrous Web formed of many randomly extending interconnected and firmly united flexible durable tough resilient organic fibrous members, said fibrous members having a diameter of from about 25 microns to about 250 microns, and abrasive particles distributed within said web and firmly bonded to fibrous members thereof by a Waterproof relatively hard rigid binder, interstices between adjacent fibrous members being open and substantially unfilled by adhesive hinder or abrasive, there being definedthroughout said article a tri-dimensionally extending network of intercommunicated voids constituting at least about of the volume of said article, said article further being flexible and readily compressible, and upon subsequent release of pressure, capable of recovering substantially completely to its initial uncompressed form.

'5. An open low-density abrasive article comprising a uniform lofty open non-woven three-dimensionally integrated fibrous web having a thickness of about onefourth inch and formed of many randomly extending interconnected and firmly united nylon fibrous members, said fibrous members having a diameter of from about 25 microns to about 250 microns, and abrasive particles distributed within said web and firmly bonded to fibrous members thereof by a hardened phenol-aldehyde resin binder, interstices between adjacent fibrous members being open and substantially unfilled by adhesive binder or abrasive, there being defined throughout said article a tri-dirnensionally extending network of intercommunicated voids constituting at least about 75 of the volume of said article, said article further being flexible and readily compressible, and upon subsequent release of pressure, capable of recovering substantially completely to its initial uncompressed form.

.6. An open low-density abrasive article comprising a uniform lofty open non-woven three-dimensional web formed of many interlaced randomly extending flexible durable tough resilient organic fibers which have a diameter of from about 25 microns to about 250 microns, web fibers 'being firmly adhesively bonded together at points where they cross and contact one another by a waterproof relatively hard rigid binder to form a threedimensionally integrated structure throughout said web, and abrasive particles distributed throughout said web and firmlybonded to web fibers by said hard rigid binder, interstices between adjacent fibers being open and substantially unfilled by adhesive hinder or abrasive, there being defined throughout said article a tridimensionally extending network of intercommunicated voids constituting at least about 75% of the volume of said article, said article further being flexible and readily compressible, and upon release of pressure, capable of recovering substantiallycompletely to its initial uncompressed form.

7. An open low-density rotary abrasive floor maintenance pad which can be employed in floor scouring or polishing operations without leaving undesirable residue as it wears through use, which is capable thereafter of being readily cleaned by simple flushing with water and then wrung out and left overnight or for days or weeks and of thenbeing reused, said pad having a depth ameter of from about 25 microns to about 250 microns 1 and which retain substantial resiliency and strength upon soaking in water, web fibers being firmly bonded to- Igether at points where they cross and contact one another by a waterproof relatively hard rigid organic binder to form a three-dimensionally integrated structure, and abrasive particles distributed throughout said web and fir'mly bonded to web fibers by globules of said binder, interstices between adjacent fibers being open and substantially unfilled by said adhesive or abrasive, there being defined throughout said pad a tri-dirn'ensionally extending network of intercommunicated voids constituting at least about 75 percent of the volume of said pad, said pad further being flexible and readily compressible, and upon release of pressure, capable of recovering substantially completely to its initial uncompressed form.

8. An open low-density rotary abrasive floor maintenance pad which can be employed in floor scouring or polishing operations without leaving undesirable residue as it wears through use, which is capable thereafter of being readily cleaned by simple flushing with water and then wrung out and left overnight or for days or weeks, and of then being re-used, said pad comprising a uniform lofty open non-woven three-dimensional web formed of many interlaced randomly extending flexible durable tough resilient fibers which have a diameter of from about 25 microns to about 250 microns and which retain substantial resiliency and strength upon soaking in water, w'eb fibers being firmly adhesively bonded together at points where they cross and contact one another to form a three-dimensionally integrated structure throughout said web, said bonding entirely over one major surface of said web and for at least a substan- 'tial depth of said web being effected by a waterproof relatively hard rigid binder, and abrasive particles dis 'tribute'd throughout the portion of said web where said ha'rd rigid binder is present With said particles being bonded to web fibers by said binder, interstices between adjacent fibers being open and substantially -unfilled by adhesive or abrasive, there being defined throughout said pad a tri-dimensionally extending network of intercommunicated voids constituting at least about 75 percent of the volume of said pad, said pad further being flexible and readily compressible, and upon release of pressure, capable of recovering substantially completely to its initial uncompressed form.

9. An open low-density abrasive article comprising a uniform lofty open non-woven three-dimensional web formed of many interlaced randomly extending flexible durable tough resilient organic fibers which have a diameter of from about 25 microns to about 250 microns, web fibers being firmly adhesively bonded together at points where they cross and contact one another to form a three-dimensionally integrated structure throughout said web, and abrasive particles distributed within said web and firmly bonded to web .fibers by a relatively hard rigid binder, said fibers having thereover a thin coating of tough flexible resilient non- :smearing material, interstices between adjacent fibers :being open and substantially unfilled by adhesive binder tor abrasive, there being defined throughout said article :a tri-dimensionally extending network of inter-communitcated voids constituting at least about 75 percent of the "volume of said article, said article further being flexible :and readily compressible, and upon release of pressure, capable of recovering substantially completely to its initial uncompressed form.

10. An open low-density abrasive article comprising a uniform lofty open non-woven three-dimensional Web formed of many interlaced randomly extending flexible durable tough resilient vorganic,fitzers which have a sliameter of from about 25 microns to about 250 microns,

web fibers being firmly adhesively bonded together at points where they cross and contact one another to form a three-dimensionally integrated structure throughout said web, and abrasive particles distributed within said web and firmly bonded to web fibers by a relatively hard rigid binder, the components of the abrasive containing web having thereover a thin coating of a tough flexible resilient non-smearing material, interstices between adjacent fibers being open and substantially unfilled by adhesive binder or abrasive, there being defined throughout said article a tri-dimensionally extending network of intercommunicated voids constituting at least about of the volume of said article, said article further being flexible and readily compressible, and upon release of pressure, capable of recovering substantially completely to its initial uncompressed form.

11. An open low-density abrasive article comprising a uniform lofty open non-woven three-dimensional web formed of many interlaced randomly extending flexible durable tough resilient organic fibers which have a diameter of from about 25 microns to about 250 microns, web fibers being firmly adhesively bonded together at points where they cross and contact one another to form a three-dimensionally integrated structure throughout said web, and abrasive particles distributed within said web and firmly bonded to web fibers by a relatively hard rigid binder, the components of the abrasive containing web having thereover a thin coating of a cured polyurethane resin, interstices between adjacent fibers being open and substantially unfilled by adhesive binder or abrasive, there being defined throughout said article a tri-dimensionally extending network of intercommunicated voids constituting at least about 75% of the volume of said article, said article further being flexible and readily compressible, and upon release of pressure, capable of recovering substantially completely to its initial uncompressed form.

12. An open low-density rotary abrasive floor maintenance pad which can be employed in floor scouring or polishing operations without leaving undesirable residue as it wears through use, which is capable thereafter of being readily cleaned by simple flushing with water and then wrung out and left overnight or for days or weeks, and of then being re-used, said pad comprising a uniform lofty open non-Woven three-dimensional web having a thickness of about one-fourth inch formed of many interlaced randomly extending flexible durable tough resilient organic fibers which retain substantial resiliency and strength upon soaking in water, web fibers being firmly adhesively bonded together at points where they cross and contact one another to form a three-dimensionally integrated structure throughout said web, said bonding entirely over one major surface of said web and for approximately one-half of the depth of said web being effected by globules of a waterproof relatively hard rigid binder, said bonding in the remaining portion of said web being effected by a resilient rubbery binder, and

abrasive particles distributed throughout the portion of said web where said hard rigid binder is present with said particles being firmly bonded to web fibers by said hard rigid binder, interstices between adjacent fibers being open and substantially unfilled by said binders or abrasive, there being defined throughout said pad a tridimensionally extending network of intercommunicated voids, said pad being highly translucent when held closely adjacent the viewers eyes under conditions where substantially all the light registering on the viewers eyes passes through the pad, said pad further being flexible and readily compressible, and upon release of pressure, capable of recovering substantially completely to its ini- ,tial uncompressed form. r

13. An open low-density rotary abrasive floor main- ;tenance pad which can be employed in floor scouring or polishing operations without leaving undesirable residue as it wears through use, which is capable thereafter of being readily cleaned by simple flushing with water and then wrung out and left overnight or for days or weeks, and of then being re-used, said pad comprising a uniform lofty open non-woven three-dimensional web having a thickness of about one-fourth inch formed of many interlaced randomly extending flexible durable tough resilient organic fibers which have a diameter of at least about 25 microns and which retain substantial resiliency and strength upon soaking in water, web fibers being firmly adhesively bonded together at points where they cross and contact one another to form a three-dimensionally integrated structure throughout said web, said bonding entirely over one major surface of said web and for approximately one-half the depth of said web being effected by globules of a waterproof relatively hard rigid binder, said bonding in the remaining portion of said Web being eifected by a resilient rubbery binder, and abrasive particles distributed throughout the portion of said web where said hard rigid binder is present with said particles being firmly bonded to web fibers by said hard rigid binder, interstices between adjacent fibers being open and substantially unfilled by said binders or abrasive, there being defined throughout said pad a tridimensionally extending network of intercommunicated voids constituting at least about 75 percent of the volume of said pad, said pad further being flexible and readily compressible, and upon release of pressure, capable of recovering substantially completely to its initial uncompressed form.

References Cited in the file of this patent UNITED STATES PATENTS 2,810,426 Till et a1 Oct. 22, 1957 

1. AN OPEN LOW-DENSITY ABRASIVE ARTICLE COMPRISING A UNIFORM LOFTY OPEN NON-WOVEN THREE-DIMENSIONAL WEB FORMED OF MANY INTERLACED RANDOMLY EXTENDING FLEXIBLE DURABLE TOUGH RESILIENT ORGANIC FIBERS WHICH HAVE A DIAMETER OF FROM ABOUT 25 MICRONS TO ABOUT 250 MICRONS, WEB FIBERS BEING FIRMLY ADHESIVELY BONDED TOGETHER AT POINTS WHERE THEY CROSS AND CONTACT ONE ANOTHER TO FORM A THREE-DIMENSIONALLY INTERGATED STRUCTURE THROUGH OUT SAID WEB, AND ABRASIVE PARTICLES DISTRIBUTED WITHIN SAID WEB AND FIRMLY BONDED TO WEB FIBERS BY A RELATIVELY HARD RIGID BINDER, INTERSTICES BETWEEN ADJACENT FIBERS BEING OPEN SUBSTANTILALLY UNFILLED BY ADHESIVE BINDER OR ABRASIVE THERE BEING DEFINED THROUGHOUT SAID ARTICLE A TRI-DIMESIONALLY EXTENDING NETWORK OF INTERCOMMUNI- 